Cardiovascular Research, 1971, 5, 416-418.
Instruments and Techniques
Experimental atrioventricular block
without thoracotomy:
a new
instrument
I. Babotai and
R.
Brownlee'
From Surgical Clinic A , University ojzurich, Switzerland
Authors' synopsis Experimental permanent total atrioventricular block was produced by
a
simplijed method, without thoracotomy, by one person, and without the aid of x-ray apparatus. For this purpose, a newly designed cannula f o r the injection of40%
formalin into the bundle of His was made.In 1968 we reported in this journal a method for experimental production of total atrio- ventricular block (Turina, Babotai, a n d Wegmann, 1968). T h e method was based o n the localization of the bundle of His with in- tracardial electrocardiogram monitoring by means of a special intravenous cannula. After bundle localization, 40% formalin was injected in the overlying myocardium, which resulted in a permanent total atrio- ventricular block. This previous method had several disadvantages. Firstly, fluoroscopy or image intensification apparatus was re- quired, and two people were needed t o operate this apparatus. Considerable prac- tice a n d facility were required before the manipulation of the complicated injection system under radiographic control could be mastered. Other recently reported methods of experimental atrioventricular block pro- duction a r e even more complicated, in that they require thoracotomy, direct intra- cardiac visualization, fluoroscopy, or a combination of these procedures (Steiner and Kovalik, 1968; Scriabine, Rival, Bellet, Morgan, Weyn, a n d Nusbaum, 1969). The newly designed cannula eliminates these problems, since the block can be created without x-ray apparatus by one person.
McLaughlin Travelling Fellow. University of
Alberta Medical Center, Edmonton 61, Alberta, Canada.
Method I Apparatus
The newly designed cannula (Fig. I ) is constructed of stainless steel tube 35 cm long and 3.5 mm in diameter. The outer cannula wall thickness is
0.5 mm and the inner cannula tip is 0.6 mm in diameter. The distal 1'5 cm of both cannulas are curved at a 45" angle. The curved end of the outer cannula has a half-round tip which acts as the intracardiac electrode and through which passes the inner needle. The entire outer cannula except for the exploring tip is electrically isolated with a coat of epoxy-resin. Attached to the proximal end of the outer cannula is a cable for
ECG monitoring. To the proximal end of the inner cannula a connector for the formalin syringe is attached. The spring loaded inner cannula is held in the retracted position by a trigger. Pressure on the trigger releases the spring loaded inner cannula and thus permits it to drive the needle tip into the myocardium when the characteristic intracardiac bundle of His potential is found (see Fig. z and Technique). The length of inner cannula protrusion following trigger depression, and thus the depth of myocardial injection, is adjustable by a screw.
z Technique
After induction of anaesthesia and tracheal in- tubation, the animal is laid left side down on the operating table. Under sterile conditions the right external jugular vein is dissected free. The can- nula with the inner tip in the retracted position, and the lumen full of 40% formalin is then intro- duced into the right atrium via a venous cut- down. The direction of the cannula tip can then be controlled by means of the flange attached to
417 Experimental atrioventricular block without thoracotomy: a new instrument 4 7 1 2
\
3 8 6 9 F I G . Iposition. I . Outer cannula with epoxy-resin isolation. 2. Inner cannula. 3. Intracardiac
exploring electrode. 4 . Spring. 5 . Trigger. 6. Depth adjustment screw. 7. Luer-lock connector for formalin syringe. 8. Flange f o r cannula tip orientation. 9. ECG cable.
Cannula for chronic A B block production. The inner cannula is in the retracted
BLOCK CANNULA
\
the distal end of the instrument. With the can- nula connected to the ECG recorder, the intra- cardiac electrocardiogram is observed while the cannula tip is manipulated. When the typical potential for the bundle of His is found (Fig. z),
the cannula trigger is depressed, thus driving the spring loaded inner cannula 3 or 4 mm into the myocardium overlying the bundle. When move- ment of the cannula meets with resistance, good positioning of the needle tip in the myocardium is ensured. Formalin 0.4 ml. is then injected. When the cannula is in good position, some resistance to injection is encountered. Immediately a total AV block should appear. If no block is seen or a partial dissociation pattern appears, more formalin can be injected, since the cannula is held in good position by the inner needle in the myocardium. After creation of a total AV block, the inner cannula is pulled back, thus with- drawing the needle from within the myocardium, and the entire instrument is removed from the heart.
Re s u I t s
T h e new instrument was used for block production in 1 1 dogs. Total AV block was
produced in 10 animals. One animal died
before the block creation because of ven- tricular fibrillation after intracardiac manipu- lation of the cannula. F o u r dogs were killed
z
hr after block creation. In six more dogs, pacemakers with intracardial electrodes were implanted after block production, in con- junction with another experiment.Histological studies of the bundle of His F I G
.
z A schematic representation ofcorrect intracardiac cannula position before formalin injection and typical intracardiac
418 Babotai and Bro wnlee
F I G . 3 Photograph of the newly designed cannula for production of experimental
atrioventricular block without thoracotomy.
after injection of formalin have been pre- viously reported by us, and are not included in this report (Turina and Babotai, 1967; Turina et al., 1968). The block became im-
mediately apparent after injection and was permanent in each instance. No long-term complications, such as congestive heart failure or tachyarrhythmia, were encountered.
Discussion
Steiner and Kovalik (1968) have reported a relatively simple and reliable method of producing total AV block which involves formalin injection through the groove be- tween the right atrium and aorta. This method eliminates the use of fluoroscopy but necessitates a right thoracotomy. Scriabine
et al. (1969), in studying drug effects on
ventricular rate in total AV block, ligated the bundle of His under direct vision. Despite the greater magnitude of the operation, suc- cessful block was produced in only about 70% of animals.
The new instrument described above is an improvement on these previously reported methods, in that a chronic atrioventricular block can be created in animals without the necessity of x-ray apparatus. When the direct-writing electrocardiogram is in close proximity to the operator, allowing ease of intracardiac electrocardiogram monitoring, the block can be produced by one person.
The spring loaded cannula needle tip
eliminates the problem of loss of correct positioning of the cannula tip during mani- pulation before formalin injection. Also, the needle goes securely into myocardium super- ficial to the bundle, so that the possibility of injecting formalin into the blood stream or outside the heart is diminished. The posi- tioning of the needle tip in the myocardium can be tested by the movement of the entire cannula. When the needle is in the myo- cardium, resistance to movement of the cannula is met. Because the entire instru- ment tip is fabricated from metal, the intra- cardiac electrocardiogram can be monitored directly during formalin injection. This feature allows a n additional assurance that the formalin injection has been properly placed.
References
Turina, M., and Babotai, I. (1967). Erzeugung eines totalen atrioventrikularen Blocks beim Hund
ohne Thorakotomie. Thoraxrhirurgk,, 15, 60 I -
608.
Turina, M . , Babotai, I, and Wegmann. W. (1968).
Production of chronic atrioventricular block in
dogs without thoracotomy. Cardiooascular Re-
search, 2, 389-393.
Steiner, C., and Kovalik, A. T. W. (1968). A simple
technique for production of chronic complete
heart block in dogs. Journal of Applied Physiology,
Scriabine, A., Rival, J., Bellet, S., Morgan. G . ,
Weyn. A. S., and Nusbaum, M. (1969). Effect
of protokylol on the ventricular rate in dogs with
experimental A-V heart block. American Heart
Journal, 77. 649-652.
